Average Migration Rate Research Articles

Satellites Reveal Global Migration Patterns of Natural Mountain Treelines during Periods of Rapid Warming

Profound global transformations in the Anthropocene epoch are hastening shifts in species ranges, with natural mountain treeline migration playing a crucial role in this overarching species movement. The varied reactions of mountain treelines to climatic conditions across diverse climatic zones, when compounded by local disturbances, result in distinct migration patterns. Usually, warming encourages mountain treelines to migrate to higher elevations. Nevertheless, in a period of rapid warming, it remains unclear whether the natural mountain treeline in global thermal climatic zones and subclimatic zones has expedited its upward movement. Here, we employed remote sensing observations and the random forest algorithm to investigate the natural treeline dynamics across 24 major mountain ranges worldwide amidst a period of rapid warming (1990–2020). Our research shows substantial disparities in the migration patterns of natural mountain treelines across the global thermal zone. The natural mountain treeline in tropical and subtropical zones descends by an average of 1.1 and 0.8 m per year, respectively. Only 18.8 and 35.5% of the natural mountain treelines in these regions had undergone upward migration, respectively. The average migration rates of natural mountain treelines in temperate and boreal zones were 0.7 m per year. Correspondingly, 47 and 33.2% of the natural mountain treelines in these zones had already shifted to higher elevations. The highest average migration rate of natural mountain treelines occurs in temperate continental climates (1.7 m per year). The loss or degradation of alpine species habitats, a direct consequence of the upward movement of the treeline, highlights the necessity for increased monitoring and protection of alpine species in temperate and boreal zones in the future.

Marsh decrease was much faster than the water increase among the Yellow River Source wetlands during 1986–2022

Wetlands are valuable and sensitive ecosystems that make them imperative to tracking the dynamics in their extent for sustainable management under global warming. Here we focused on the Yellow River Source (YRS) wetlands, which is renowned for hosting one of the world's largest plateau peat bog, unfortunately, it had experienced sharp degradation, threatening the safety of water supply for approximately 110 million people of the lower Yellow River basin. However, the lack of long-term, dense time-series data makes it challenging to assess its evolution trends and driving factors. Therefore, we developed a decision tree sample migration method based on Euclidean distance and Land Surface Water Index, and successfully generated annual wetland mapping of YRS from 1986 to 2022 by utilizing the Landsat 5/7/8 datasets and Random Forest method. The average sample migration rate was 89.21 %, with an average overall accuracy of 95.49 %. We observed that the marsh area decreased by 2031 km2, marking a decline of 12.98 %, while the water area increased by 710 km2 (31.24 %) compared to 1986. Spatially, 10.96 % of marsh composition presents significant (P < 0.05) decline trend, which are mainly converted to grass (86 %), followed by impervious (10 %). There were 6.69 % of water composition showing significant (P < 0.05) increase trend, which are mainly sourced from impervious (82 %) and marsh (12 %). Grazing activities were more important driving forces than climate change for marsh degradation, while the water expansion was associated with recent rising temperature in YRS. The sample migration method is proved to be feasible, robust, and effective for long-term wetland mapping. We suggest that wetland decision-makers need to focus on marsh degradation and reduce grazing intensity, so that fostering the sustainable and healthy wetlands in the Qinghai-Tibetan Plateau.

Grain boundary migration and mechanical properties altering in Fe – 10Ni – 20Cr alloy under irradiation

Mechanisms of ∑5(210)[001] and ∑5(310)[001] symmetrical tilled grain boundaries migration in bicrystall Fe – 10Ni – 20Cr samples under irradiation were investigated by means of molecular dynamics. The density of radiation defects grows quite quickly up to a dose of ~0.02 dpa and then reaches saturation. This is due to balancing of the radiation defects generation and annihilation rates. It is shown that at the early stage of irradiation, grain boundaries began to deviate stochastically from their initial positions due to interaction with cascades of atomic displacements and absorption of structural defects. During irradiation, the grain boundary region thickened and became rough. With an increase in the radiation dose, size of the clusters of point defects (tetrahedrons of stacking faults and dislocation loops) increased. Interaction with large clusters of point defects led to the formation of bends on initially flat surfaces of grain boundaries. At small distances between the boundaries, the high driving force between the curved surfaces of grain boundaries significantly increased the rates of their approach. The average migration rates of grain boundaries before their direct interaction with each other were approximately 0.8 m/s. As a result of their approach, the grain boundaries were annihilated, the potential energy of the sample decreased abruptly, and the grains merged. The annihilation of grain boundaries ∑5(310)[001] required twice the radiation dose compared to the grain boundary ∑5(210)[001]. The direct interaction of grain boundaries with each other abruptly increased the velocity of their migration due to the emergence of a driving force from the curved sections of the grain boundary surfaces. Influence of the radiation dose on deformation behavior features of the samples under uniaxial strains was studied. With an increase in the radiation dose, the elastic limit decreased rapidly and reached saturation at an irradiation dose of ~0.01 dpa.

Migration characteristics and risk assessment of chemical hazardous substances in infant teether toys

Teether is a special toy used for infants oral contact. In this paper, a residual and migration detection method was developed using gas chromatography–tandem mass spectrometry for 20 screened hazardous substances in teethers. Fifteen substances were detected in 59 samples, with residual amounts and detection rates ranging from 0.01 mg⋅kg−1 to 106.15 mg⋅kg−1 and from 3.39 % to 84.7 % respectively. Then, 12 substances were detected in simulated saliva at migration levels ranging from 0.0143 mg⋅kg−1 to 20.03 mg⋅kg−1, with detection rates ranging from 1.69 % to 76.3 %. Statistically, the average migration rate of each substance ranged from 8.18 % to 53.28 % depending on the properties of the substance and the sample. The exposure risk of infants to teethers was evaluated separately for two age groups. The hazard quotient (HQ) and hazard index (HI) values for the analytes were higher in the 3–12-month age group than in the 12–24-month age group. The HQ values of triphenylphosphine oxide, benzocaine, and N-methylformanilide were relatively high, with averages of 1.2 × 10−2, 2.5 × 10−3, and 1.6 × 10−3, respectively, and the max HI of the 12 substances was 0.04. The HI and HQ values of the analytes were all below 1, indicating that the non-carcinogenic risks of analytes in teethers are at an acceptable level.

The Style Transformation of Gu-Zheng Music Based on the Improved Model of Cyclegan

In recent years, generative adversarial networks have excelled in the field of image style migration, however their performance in the field of music has been mediocre. Existing music style migration does not work well for style migration of gu-zheng music. In order to solve these problems, we first extract the features of gu-zheng music and the Mel-spectrum features, then use CycleGAN to do style transformation on the combined features and Mel-spectrum features, and then use WaveNet vocoder to decode the migrated spectrograms, and finally achieve the style migration with gu-zheng music. The proposed model was evaluated on the publicly available dataset FMA, and the average style migration rate of the compliant music reached 94.07%. Compared to other algorithms, the music produced by this method outperformed other algorithms in terms of style migration rate and audio quality.

The Style Transformation of Gu-Zheng Music Based on the Improved Model of Cyclegan

In recent years, generative adversarial networks have excelled in the field of image style migration, however their performance in the field of music has been mediocre. Existing music style migration does not work well for style migration of gu-zheng music. In order to solve these problems, we first extract the features of gu-zheng music and the Mel-spectrum features, then use CycleGAN to do style transformation on the combined features and Mel-spectrum features, and then use WaveNet vocoder to decode the migrated spectrograms, and finally achieve the style migration with gu-zheng music. The proposed model was evaluated on the publicly available dataset FMA, and the average style migration rate of the compliant music reached 94.07%. Compared to other algorithms, the music produced by this method outperformed other algorithms in terms of style migration rate and audio quality.

Horizontal Rates of Wetland Migration Appear Unlikely to Keep Pace with Shoreline Transgression under Conditions of 21st Century Accelerating Sea Level Rise along the Mid-Atlantic and Southeastern USA

This investigation evaluated two fundamental assumptions of wetland inundation models designed to emulate landscape evolution and resiliency under conditions of sea level rise: that they can (1) migrate landward at the same rate as the transgressing shoreline and (2) immediately replace the plant community into which they are onlapping. Rates of wetland (e.g., marsh, mangrove) migration were culled from 11 study areas located in five regions of focus: Delaware Bay, Chesapeake Bay, Pamlico Sound, South Florida, and Northwest Florida. The average rate of marsh migration (n = 14) was 3.7 m yr−1. The average rate of South Florida mangrove migration (n = 4) was 38.0 m yr−1. The average rate of upland forest retreat (n = 4) was 3.4 m yr−1. Theoretical rates of shoreline transgression were calculated using site-specific landscape slope and scenario-based NOAA sea level rise elevations in 2050. Rates of shoreline transgression over the marsh landscape averaged 94 m yr−1. The average rate of shoreline transgression in the mangrove-dominated areas of South Florida was 153.2 m yr−1. The calculated rates of shoreline transgression were much faster than the observed horizontal marsh migration, and by 2050, the offset or gap between them averaged 2700 m and ranged between 292 and 5531 m. In South Florida, the gap average was 3516 m and ranged between 2766 m and 4563 m. At sites where both horizontal marsh migration and forest retreat rates were available, the distance or gap between them in 2050 averaged 47 m. Therefore, the results of this study are inconsistent with the two fundamental assumptions of many wetland inundation models and suggest that they may overestimate their resilience under conditions of 21st century accelerating sea level rise.

Rapid migration of Mongolian oak into the southern Asian boreal forest.

The migration of trees induced by climatic warming has been observed at many alpine treelines and boreal-tundra ecotones, but the migration of temperate trees into southern boreal forest remains less well documented. We conducted a field investigation across an ecotone of temperate and boreal forests in northern Greater Khingan Mountains of northeast China. Our analysis demonstrates that Mongolian oak (Quercus mongolica), an important temperate tree species, has migrated rapidly into southern boreal forest in synchrony with significant climatic warming over the past century. The average rate of migration is estimated to be 12.0 ± 1.0 km decade-1 , being slightly slower than the movement of isotherms (14.7 ± 6.4 km decade-1 ). The migration rate of Mongolian oak is the highest observed among migratory temperate trees (average rate 4.0 ± 1.0 km decade-1 ) and significantly higher than the rates of tree migration at boreal-tundra ecotones (0.9 ± 0.4 km decade-1 ) and alpine treelines (0.004 ± 0.003 km decade-1 ). Compared with the coexisting dominant boreal tree species, Dahurian larch (Larix gmelinii), temperate Mongolian oak is observed to have significantly lower capacity for light acquisition, comparable water-use efficiency but stronger capacity to utilize nutrients especially the most limiting nutrient, nitrogen. In the context of climatic warming, and in addition to a high seed dispersal capacity and potential thermal niche differences, the advantage of nutrient utilization, reflected by foliar elementomes and stable nitrogen isotope ratios, is also likely a key mechanism for Mongolian oak to coexist with Dahurian larch and facilitate its migration toward boreal forest. These findings highlight a rapid deborealization of southern Asian boreal forest in response to climatic warming.

Dune movement under climatic changes on the north‐eastern Tibetan Plateau as recorded by long‐term satellite observation versus ERA‐5 reanalysis

AbstractThe movement of active dunes is tightly linked to climatic conditions (e.g., wind regime, temperature and precipitation) as well as human influence (e.g., grazing, dune fixation and greening). Dune migration rates can be studied to draw conclusions of changing wind conditions over time. The Gonghe Basin (GB), located on the north‐eastern Tibetan Plateau (TP), offers a good testing ground for these assumptions. The intramontane basin is highly influenced by two major wind regimes: the mid‐latitude Westerlies and the East Asian summer monsoon. To investigate environmental changes, this study combines optical remote sensing techniques with climatic datasets. High‐resolution satellite images of the last five decades, such as CORONA KH‐4B, are used to map dunes and calculate their respective migration rates. Further, height information was extracted as well. Climatic changes from the ERA‐5 reanalysis dataset and normalized difference vegetation index (NDVI) values were processed alongside. Relating the dunes' surface processes to climate model data shows an accordance between slowing migration, expanding vegetation and a decrease in sand drift potential. From 1968 to present time, an average dune migration rate of 7.3 m a−1 was extracted from the satellite images, with an overall reduction of −1.81 m a−1. The resultant drift potential (RDP) values for the GB are calculated to be below 10 m3 s−3 with a spatial decrease, following a direction from the NW to the SE, fitting well with a corresponding decrease in the migration rates. Our results indicate a good agreement between the development of aeolian landforms and the ERA‐5 climate reanalysis model data, even in a high‐altitude setting with complex topography, which is known to influence such datasets.

Dune migration at Canoa Quebrada, northeast Brazil

In the coastal area of Ceará State, northeast Brazil, there are large mobile dunefields, including barchans, barchanoid dunes and sandsheets. The migration rate of these dunes, as measured by several studies, varies between 32 m/y and 9 m/y. This paper analyzes the migration of the dunes in Canoa Quebrada Beach, located in the eastern coast of Ceará State, using remote sensing of aerial photos and satellite imagery from 1988 to 2013 (25 years). The resulting data indicate an average migration rate varying from 1.8 m/y to 9.3 m/y. This is the lowest rate of migration measured for large and undeveloped mobile dunes in Ceará State. The analysis indicates that the element responsible for this low rate is the low wind speed. However, the installation of wind power turbines in the area – which demanded the fixation of part of the dunes to prevent the equipment from being buried and from aeolian erosion – might be another reason for the decreasing dune migration. The dune migration decrease may increase the sedimentary deficit in the coastline downdrift of Canoa Quebrada Beach.

Temporal analysis of the planform morphology of the Quevedo River, Ecuador, using remote sensing

This study aims to characterize the channel morphology and dynamic changes of the Quevedo River during 1986–2019 using Landsat and Sentinel satellite images. We classified around one hundred bends within a 125 km long section of the river into simple and compound bends. We measured their morphometric parameters: bend length, channel width, the radius of curvature, and sinuosity index (SI). Quevedo River showed a decrease in sinuosity and its total length (−3.7 km), mainly caused by cutoffs. Then, we compared the sequential positions of 50 bends or meanders (bends with SI > 1.25) in 1986–2000 and 2000–2019 to classify their change patterns and measure their migration's distance, rate, and direction. We found that migration patterns were dominated by translation and extension of bends and the presence of two differentiated reaches. The northern reach presents average migration rates four times higher than the southern one (7.1 vs. 1.7 m/year). Along with the observed decrease in sinuosity, there is a generalized decrease in migration rates, which might be attributed to the construction of the Baba Dam upstream of the river. Finally, we found that migration rates were maximum in meanders with medium curvatures. These findings can contribute to improving river management and implementing policies to increase local communities' resilience to river hazards.

Shifting Sands: Assessing Bankline Shift Using an Automated Approach in the Jia Bharali River, India

Bank erosion hazard is a frequent occurrence that poses threats to floodplain ecosystems. This analysis examined changes to the Jia Bharali River channel in India using the GIS-based Digital Shoreline Analysis System [DSAS]. The Jia Bharali’s future channel was predicted so as to identify the most erosion-susceptible zones. The rate of bankline movement was calculated using remotely sensed data collected over a period of 45 years (1976–2021). The results show that the river’s erosion and deposition rates were higher in the early years than towards the later part of the period under analysis. On the right and left banks of the river, the average shift rate was −9.22 and 5.8 m/y, respectively, which is comparatively high. The chosen portion of the river was evenly divided into three zones, A, B, and C. The most positively affected zone was zone A. The left bank of zone B exhibited a higher rate of erosion than the right bank, indicating that the river was moving to the left [eastward] in this zone. At the same time, the right bank was being eroded faster than the left, indicating a westward thrust at zone C. The predicted result demonstrates that the left bank of zone B and the right bank of zone C would have a higher average migration rate. Therefore, these banks were identified as being the most susceptible to bank erosion. The study evaluates the spatio-temporal change of the river in sensitive regions where neighboring settlements and infrastructure were at risk of changing channel dynamics. Using the actual and forecasted bankline, the degree of accuracy was confirmed. The results of the automated prediction approach could be useful for river hazard management in the Jia Bharali and in similar environmental settings with tropical high precipitation zones.

Anthropogenic channel network development in forested watersheds by recent stream channelization practices in Mark Twain National Forest, Missouri Ozarks

Human modifications of stream systems often result in channel instability and sediment pulse- induced problems. While previous research explored the direct anthropogenic impacts of channelization on fluvial systems, the history of repeated channelization, their persistent impacts on headwater streams and subsequent evolution of a drainage system need further investigation. This study evaluates the spatial distribution of channel form and stability in Big Barren Creek watershed, which drains the karst dominated Ozark Highlands of southeast Missouri. The objectives of this research are threefold: (i) describe channel morphology and hydrology in undisturbed and disturbed segments based on field data, (ii) propose a conceptual model of channel modification and response to explain the patterns of channel adjustment and (iii) evaluate the history of channel disturbance using historical aerial photograph analysis. Results show that disturbed reaches have larger channel dimensions than undisturbed reaches because channelization increased stream power and shear stress, particularly for channels that are actively incising. Channelized reaches are primarily identified on private land where headcuts developed and migrated upstream to the national forestland. Sediment supply to the channel increases from both upstream incision and bank and levee collapse resulting in downstream aggradation, which forces landowners to repeat channelization for flood control. The proposed conceptual model suggests that while the disturbed segments evolve into wider and deeper channels following channelization, they exhibit the potential to become stable over time because of biogeomorphic resistance (e.g., in-channel vegetation, armored-cohesive soil) related to the ephemeral nature of the streams in this karst region. This idea is also supported by the slower average headcut migration rate of earlier channelization (2 m/yr) compared to recent channelization (6–8 m/yr). However, channel adjustment largely depends on repeated channelization that resets the evolutionary stages that preclude this fluvial system from attaining stability.

The Role of the Adapter Protein Anks1a in the Regulation of Breast Cancer Cell Motility.

Epithelial-mesenchymal transition (EMT) is a critical step in tumor progression that leads to the acquisition by cancer cells the capacity for migration using the mesenchymal motility mode regulated by the Rac→WAVE→Arp2/3 signaling pathway. Earlier it was shown that proteins interacting with Rac can regulate mesenchymal migration and thus determine the metastatic potential of the cells. The search for new regulators of cell migration is an important theoretical and practical task. The adaptor protein Anks1a is one of the proteins interacting with Rac, whose expression is altered in many types of tumors. The aim of this study was to find whether Anks1a affects the migration of cancer cells and to identify the mechanism underlying this effect. It was suggested that Anks1a can influence cancer cell migration either as a Rac1 effector or by activating human epidermal growth factor receptor 2 (HER2) exchange. We investigated how upregulation and inhibition of Anks1a expression affected migration of breast cancer cells with different HER2 status. Anks1a was shown to interact with the activated form of Rac1. In the MDA-MB-231 cells (triple negative cancer), which lack HER2, Anks1a accumulated at the active cell edge, which is characterized by enrichment with active Rac1, whereas no such accumulation was observed in the HER2-overexpressing SK-BR-3 cells. Downregulation of the ANKS1a expression with esiRNA had almost no effect on the cancer cell motility, except a slight increase in the average migration rate of MDA-MB-231 cells. Among three cell lines tested, overexpression of Anks1a increased the migration rate of HER2-overexpressng SK-BR-3 cells only. We showed that Anks1a is an effector of activated Rac1, but its influence on the cell migration in this capacity was minimal, at least in the studied breast cancer cells. Anks1a affected the motility of breast cancer cells due to its involvement in the EGF receptor exchange.

Towards an understanding of future range shifts in lichens and mosses under climate change

AbstractAimLichens and mosses play important functional roles in all terrestrial ecosystems, particularly in tundra and drylands. As with all taxa, to maintain their current niche in a changing climate, lichens and mosses will have to migrate. However, there are no published estimates of future habitat suitability or necessary rates of migration for members of these groups at the global scale.TaxonLichens and mosses.LocationGlobal.MethodsUsing global occurrence data, we conducted ensemble distribution models in the ‘biomod2’ R package, parameterised with a range of climatic, land use and soil variables, to estimate current and future (2100) habitat suitability in 16 abundant species of lichen and moss.ResultsWithout considering dispersal limitation, suitable area was forecast to expand for eight species and decline for four species. For species with predominantly boreo‐arctic distributions, suitable area typically declined at the temperate range edge and expanded across the High Arctic. Future suitable area available to dryland‐adapted species generally declined overall, likely relating to the desiccation‐tolerant physiology of lichens and mosses. The average migration rates required for species to disperse into new suitable habitat ranged from 1.7 (Placidium squamulosum) to 9.0 km year−1 (Syntrichia ruralis), although most species will need to migrate &gt;16 km year−1 to completely fill their potential future suitable habitat.Main ConclusionsFor mosses and lichens, as with all species, migration will be an important part of the adjustment to a warmer climate, but realisation of these potential migrations will require both rare dispersal events and habitat that is suitable in non‐climatic dimensions. Current evidence on dispersal in these groups suggests that these geographical shifts may be unlikely to be realised without intervention, especially in landscapes that are highly modified by humans.

Conservation genomics of Agave tequilana Weber var. azul: low genetic differentiation and heterozygote excess in the tequila agave from Jalisco, Mexico.

Genetic diversity is fundamental for the survival of species. In particular, in a climate change scenario, it is crucial that populations maintain genetic diversity so they can adapt to novel environmental conditions. Genetic diversity in wild agaves is usually high, with low genetic differentiation among populations, in part maintained by the agave pollinators such as the nectarivorous bats. In cultivated agaves, patterns of genetic diversity vary according to the intensity of use, management, and domestication stage. In Agave tequilana Weber var. azul (A. tequilana thereafter), the plant used for tequila production, clonal propagation has been strongly encouraged. These practices may lead to a reduction in genetic diversity. We studied the diversity patterns with genome-wide SNPs, using restriction site associated DNA sequencing in cultivated samples of A. tequilana from three sites of Jalisco, Mexico. For one locality, seeds were collected and germinated in a greenhouse. We compared the genomic diversity, levels of inbreeding, genetic differentiation, and connectivity among studied sites and between adults and juvenile plants. Agave tequilana presented a genomic diversity of HT = 0.12. The observed heterozygosity was higher than the expected heterozygosity. Adults were more heterozygous than juveniles. This could be a consequence of heterosis or hybrid vigor. We found a shallow genetic structure (average paired FST = 0.0044). In the analysis of recent gene flow, we estimated an average migration rate among the different populations of m = 0.25. In particular, we found a population that was the primary source of gene flow and had greater genomic diversity (HE and HO ), so we propose that this population should continue to be monitored as a potential genetic reservoir. Our results may be the consequence of more traditional management in the studied specific region of Jalisco. Also, the exchange of seeds or propagules by producers and the existence of gene flow due to occasional sexual reproduction may play an important role in maintaining diversity in A. tequilana. For populations to resist pests, to continue evolving and reduce their risk of extinction under a climate change scenario, it is necessary to maintain genetic diversity. Under this premise we encourage to continue acting in conservation programs for this species and its pollinators.

Assessment of meander‐bend migration of a major distributary of the Ganges River within Bangladesh

AbstractThe Arial Khan is an important distributary river of the Ganges River within Bangladesh. The river is meandering, and channel shifting and bend migration are common. This study investigates the bend‐scale morphology of 37 characteristic bends of the river using Landsat imageries, river bathymetries, and hydrological data. The morphological changes of the river are correlated with the temporal shifting of its offtake, which in turn is linked to the dynamic behavior of the river in terms of sinuosity, bend geometry, and bend migration. Alterations in the offtake location, bed elevation, and in‐front bar formation are found to control the flow to the river. The sinuosity varies from 1.62 to 1.95 and is linked to the shifting of its offtake. The lifetimes of the bends increase from upstream to downstream with an average lifetime of 24 years. The radii of the bends vary from upper to lower reaches with an average radius of 921 m. The upper reach is more migration prone, and its average migration rate (108 m/year) is more than twice the other two reaches. A higher migration rate of 70–80 m/year is found for the river during 1981–1999 compared to the rates of 45–50 m/year for the rest of the study periods (1972–2021). An envelope curve depicting the relation between the relative curvature of a bend and its migration rate for the river is also developed. The overall morphology from 1972 to 2021 indicates that a significant increase in sinuosity and a reduction in river width and aspect ratio have occurred. The migration rate has declined slightly and the frequency of bend cutoffs has reduced notably in recent years. Nonetheless, due to the high rates of migration, there exists potential future threat to riverbank erosion in some critical bends, and hence damages to land, property, structure, and project on the vulnerable banks.

Effects of time, temperature, and sebum layer on migration rate of plasticizers in polyvinyl chloride products

Large amounts of plasticizers, such as di(2-ethylhexyl) phthalate (DEHP) and dioctyl terephthalate (DOTP), are added to various polyvinyl chloride (PVC) products. To assess the human exposure to these plasticizers on using PVC products, it is important to know their migration rate. However, conventional migration tests conducted at a fixed time and temperature are often insufficient for determining possible variations in migration rates with respect to time, temperature, and sebum layer. In this study, the migration rates of DEHP and DOTP from five PVC products were measured using a polydimethylsiloxane (PDMS) sampler at different times and temperatures, in the presence and absence of artificial sebum. Although the migrated mass of the plasticizers increased over time, the average migration rate decreased. The average migration rates increased with increasing temperature and in the presence of an artificial sebum layer between the product and the PDMS sampler. When the artificial sebum layer was added, the average migration rate increased considerably by a factor of 1.5–14, suggesting that sebum should be considered to avoid the underestimation of dermal exposure to highly hydrophobic plasticizers, such as DEHP and DOTP. Based on the measured values, a conceptual analysis was conducted to quantitatively assess the difference in the migration rate of plasticizers caused by the difference between the time set for the migration test and the exposure time when the product is used. To reduce uncertainties and the potential underestimation of dermal exposure, an appropriate time for the experiment should be set to simulate the exposure scenario of a given product.

Study on the migration performance of Cs(I) in the treatment of simulated radioactive wastewater by electrodialysis.

As a competitive radioactive wastewater treatment technology, electrodialysis (ED) has the advantages of low operating pressure and high cycles of concentration. In order to analyze the migration performance of radionuclides during the treatment of radioactive wastewater by ED, a radionuclide migration model was constructed based on the mass conservation law and Faraday's law with the typical radionuclide cesium as the research object. Experiments were carried out for the treatment of simulated radioactive wastewater in a small-scale ED system, and the average migration rate of radionuclides under different operating conditions was predicted by the model. The results showed that the experimental values of concentration and average migration rate of Cs(I) were significantly correlated with the calculated values of the model, in which the relative error of the average migration rate was 4.54%. The variation characteristics of Cs(I) concentration in diluted solution under different current and volume ratio conditions can be predicted by the model. The average variation rate of Cs(I) concentration decreases significantly with the increase of current and volume ratio.

Evolutionary Genomics of a Subdivided Species.

The ways in which genetic variation is distributed within and among populations is a key determinant of the evolutionary features of a species. However, most comprehensive studies of these features have been restricted to studies of subdivision in settings known to have been driven by local adaptation, leaving our understanding of the natural dispersion of allelic variation less than ideal. Here, we present a geographic population-genomic analysis of 10 populations of the freshwater microcrustacean Daphnia pulex, an emerging model system in evolutionary genomics. These populations exhibit a pattern of moderate isolation-by-distance, with an average migration rate of 0.6 individuals per generation, and average effective population sizes of ∼650,000 individuals. Most populations contain numerous private alleles, and genomic scans highlight the presence of islands of excessively high population subdivision for more common alleles. A large fraction of such islands of population divergence likely reflect historical neutral changes, including rare stochastic migration and hybridization events. The data do point to local adaptive divergence, although the precise nature of the relevant variation is diffuse and cannot be associated with particular loci, despite the very large sample sizes involved in this study. In contrast, an analysis of between-species divergence highlights positive selection operating on a large set of genes with functions nearly nonoverlapping with those involved in local adaptation, in particular ribosome structure, mitochondrial bioenergetics, light reception and response, detoxification, and gene regulation. These results set the stage for using D. pulex as a model for understanding the relationship between molecular and cellular evolution in the context of natural environments.